To sleep, perchance to roam

You jolt awake, sensing a presence in your room. Heart racing, you open your eyes and the figure comes into focus. Her glassy eyes seem to stare right through you. You sigh thinking, “not again,” and take your sleepwalking child back to bed.

Sleepwalkers are stereotypically portrayed wandering about with the same outstretched arms and unintelligible murmurs as the undead antagonists in a bad zombie movie. Nocturnal adventurers aren’t nearly as dangerous, but can certainly cause distress for themselves and others. While sleepwalkers often awake feeling refreshed, the startling encounter can leave their bed partners or caregivers restless (sorry, Mom!)

Fairly common in young people (one study found 45% of children aged 4-16 had sleepwalked [1]), sleepwalking is usually thought of as a phase children grow out of, with peak prevalence around 10 years of age [2]. However, up to 4% of adults sleepwalk; in the U.S. that roughly equals the population of Pennsylvania. These episodes can occur with varying frequency, from less than once a year up to three times a week, and each lasts about 10-30 minutes [1, 3]. Sleepwalking can range in complexity from sitting up in bed to more involved tasks; some people (me) wake up to discover every pair of socks they own littering the floor, the drawer the socks usually occupy ransacked. Were the socks thrown in a furious search for something beneath them or simply discarded one by one until the perfect pair was found? It’s hard to say because, like most people who sleepwalk, I don’t remember anything about these events [4]. In fact, one thing that makes this behavior so difficult to study is the reliance on witnesses or self-report upon waking to an unusual scene in the morning.

Half Asleep

We typically think of sleep and wake as distinct states, but sleepwalkers seem to posses layered characteristics of each. A normal sleeper will cycle through stages of non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep throughout the night. REM sleep is characterized by patterns of brain activity that most closely resemble wakefulness, vivid dreams, and temporary paralysis so you don’t act out those dreams. NREM sleep can be subdivided into stages with specific electroencephalogram (EEG) activity. Increasing numbers reflect deeper sleep, with stage 3 representing deep, slow-wave sleep during which the sleeper is the hardest to wake. Most periods of slow-wave sleep occur during the first third of the night, whereas the longest periods of REM take place during last third of the night [1, 2].

Distribution of different sleep stages across a typical night in healthy individuals from [2]

Sleepwalking is a NREM sleep disorder, usually occurring during stage 3 [2]. Sleepwalking has been described as a disorder of arousal in which the brain, rather than transitioning between these stages normally, tries to jump directly from slow-wave sleep to wakefulness [5]. The result is a sleep/wake hybrid state. Half of EEG recordings in sleepwalking adults show delta activity (the characteristic feature of stage 3, slow-wave sleep), which can appear with theta activity (found in stages 1 and 2) and intermixed or overlaid alpha and beta activity (associated with wakefulness) [6]. Patterns of alpha and beta activity with intermixed theta activity have also been observed [6]. Together, this suggests an incomplete wakefulness where sleepwalkers are neither truly awake nor fully asleep. This calls into question whether sleep and wake are as distinct as we think. Several studies have even found evidence for local sleep in individual brain regions, rather than uniform, global sleep or wakefulness throughout the brain [2, 5], a concept that is taken to a whole new level in the unihemispheric sleep of certain animals.

Sleepwalking runs in families, suggesting a genetic component, and both internal (e.g. apnea, when a person stops breathing during sleep) and external (e.g. noise) factors, as well as a number of potential triggers like sleep deprivation and alcohol use can precipitate an event in a predisposed individual [4]. Sleepwalking tends to be somewhat mundane and resolves on its own in childhood [1]. Until then, little typically needs to be done apart from eliminating potential triggers (e.g. napping to combat sleep deprivation) and mitigating potential harm (e.g. sleeping on the lowest floor of the house, padding bedside furniture, removing weapons or dangerous items) [1,4].

Other things that go bump in the night

Confusional arousals and sleep terrors also fall under the category of NREM sleep disorders, similarly occurring during stage 3 sleep in the first third of the night. During a confusional arousal, a child will typically appear distressed as if just woken up, and may even cry, but will be completely inconsolable [1]. Perhaps most alarming, sleep terrors involve blood-curdling screams from a flushed, sweating child whose heart is racing and who is possibly thrashing or even running away from a perceived threat [1]. As with confusional arousals, no amount of parental effort can soothe the child. Yes, I had those too; in fact most children will have at least one NREM sleep disorder at some point [2].

Unlike NREM disorders, REM sleep behavior disorder (RBD) typically presents in adults, not children. RBD results from a lack of paralysis during REM sleep. No longer immobilized, the individual is able to act out his dreams, which can be incredibly dangerous. Once awake, these individuals are often able to recall the dream being enacted. There is a strong relationship between RBD and neurodegeneration; one study found that at 14 years post RBD diagnosis the estimated risk of a neurodegenerative disease diagnosis was over 90% [7]. This appears to be related to the abnormal aggregation of alpha synuclein protein, with predominant diagnoses of dementia with Lewy bodies, Parkinson disease and multiple system atrophy [7]. To learn more about the perils of misplaced paralysis, check out this post.

“Maybe you shouldn’t live in food!”— a nonsensical reprimand uttered by, you guessed it, me again.

While you were sleeping

It’s interesting to consider the ethical implications of existing in the hybrid space between sleep and wake. If you’re unaware of your nocturnal wanderings, are you accountable for what you do? Despite the typically benign nature of childhood sleepwalking, adult NREM sleep disorders have a large potential for undesirable situations and even serious harm. Sleep-related eating disorders not only involve an out-of control binge, sometimes of toxic items, but come with the additional dangers of using sharp knives or gas burners [4]. Sleep sexual behaviors can also occur, ranging in severity from vocalizations to sexual assault [4]. Sleepwalking has even been used as a defense for murder.

Twenty-three year old Kenneth James Parks drove over 14 miles to his in-laws home and stabbed his mother-in-law to death after attacking his father-in-law [8, 9]. He then drove to the police station to turn himself in. Parks had a gambling problem, attempted to recover financially by embezzling at work, and had been fired. He had confessed to his wife and the two planned to visit his in-laws the next day to tell them about his gambling and their financial problems. His sleep deprivation, along with a history of sleepwalking and subsequent sleep studies showing EEG activity characteristic of sleepwalkers, both a lack of motive and grief over what happened, and his consistent reports of amnesia for the events supported his sleepwalking argument [8]. Parks was acquitted and the Canadian Supreme Court later upheld the decision. If your first thought is, “This would make an excellent lifetime movie,” the made-for-TV special “The Sleepwalker Killing” beat you to it.

Though usually innocuous, cases like Parks’ highlight the need for a more comprehensive understanding of sleepwalking and other NREM sleep disorders. Thankfully for the rest of us, socks can be returned to their drawer and the éclairs aren’t usually poisoned.